What if you replace the battery in your motorcycle with Nicd's/Nimh's?

My doctor for the past 10 yrs knows all about my addiction to battery powered airplanes. He called me up yesterday and asked me about an idea he had. He wants to up the speed at which his dirt bike onboard starter cranks. This is to speed up starting it in the "Hair and Hound" series of offroad motorcycle racing he enjoys. They do a "Le Mans" style start with the engines dead. He thinks this'll give him a "Hole Shot" ahead of the pack.

A few questions:

What if he were to use lets say a 14 cell battery pack. I'm sure the starter motor would crank faster, but will the charging system charge the pack?

What is going to happen to the cells? Will they take this sort of use?

Another question, what would happen to the electronic ignition and other electronics at the higher voltage? Will they handle the tasks at a higher than stock voltage?

The short answer is a big fire. The long answer is that the batteries are completely incompatible with the charging/starting system in the bike. You think your planes use a lot of amps? That's not even the throw of the solonoid. Lead acids do best in these conditions. If he wants it to crank faster he should look to some other way to boost the voltage to the starter but accept that the starter isn't going to last and may STILL cause a fire.

I'm not sure that it will help him anyways. He should look for other short-cuts to starting. Keeping the engine in perfect tune with a new spark plug is one way. Boost the voltage at the plug. Starter fluid? Run the engine good and hot ahead of time so that it is a hot start, too.

If it is a true lemans start he will run from a predetermined point. Tell him to give himself a physical and run faster
Do what we used to do at our road race club days when at the end of the day we had an all in lemans race at the end of the day.
Find your main competition, (normally the one with the most money) and sabotage . Put it in top gear, pull off a plug lead, turn off their fuel ( I liked that one the best )

While I have not tried it, I beg to differ from windsurfer.
I can't see any reason why nicads would not work in a bike.
The starter can handle a little extra voltage, it will just spin faster. We are not talking 24 volts here, just a little extra.
The charging system is generally putting out 14.5V or so, and you can take the battery out of the system and run all day like that, just off the alternator, so I guess the electronics are not a problem. Charging, well, you can adjust the voltage regulator.
Suggest you make up a pack and see how fast it cranks the starter...if it is any gain with 14-16 volts, is it worth messing with.
I ride motorcycles pretty much every day, I know a bit about them, and I can't see why this would be an "instant fire".

Modern vehicle electronics don't like being run without a battery.
You can take out the battery on some bikes but you will need a capacitor to dampen it down a bit, some dirt bikes come this way std. XR250/600s huskys and the like, But then you have no starter power so it defeats the purpose.
As far as adjusting the regulator/rectifier, unless you have an old triumph or an xs650 yamaha that had adjustable seperate regulators, you can't do didly to them without digging out all the resin.

Given the length of these types of races, saving .05 of a second is much more easily had by simply improving his riding.

I just wanted to add that John is is in excellent health and works out quite a bit (BTW, he races in the senior class). The reason he wants this is that he says they get 50 or more racers per race and it helps to get out in front of as many as possible as fast as possible so he doesn't have to eat more dust than he needs to.

Another idea, how about this. What if he left the battery alone and rewound the armature on that starter motor with fewer winds? That should allow a higher cranking speed, wouldn't you think?

If you really intend to do this project then the first item on the list is to get accurate current readings on the starter motor under worse case mechanical load. Then approximate the current at the revised target voltage or motor winds.

With that data, you can determine what NiCD cell or Lead Acid battery would be needed to handle the increased currents. There is a chance that the battery weight penality will offset the meager time savings that are gained.

If you use 14 cell NiCD pack then you will need to redesign the charge system. This is not a huge deal if you have some electronics experience. It may be possible to skip on-the-road recharging and instead rely on a field charger after each race.

I have a feeling that little will be gained in this effort, but then I haven't raced a motorcycle.

In the most recent Popular Mechanics there is an annoucement about permanent magnet starter motors. www.proformparts.com
That might be your best bet. Supposedly lighter and have more torque.

Really though, if your bike starts on the first crank (which it should if tuned just right) it won't matter how much you tweak the starter system it'll only make a fraction of a second difference to any start you try.

BTW if you just want the starter to crank faster reduce the gearing on it. Or you could try a 6-volt starter if that is a 12 volt bike. Plan on going through starters though.

And gouch is right that trying to run without a battery can destroy the electronics in a modern motor vehicle. While I don't have any experience with motorcycles in particular I have seen cars where the computers got fried from trying this.

O.K., now that opens a whole NEW can of worms. Starting the bike in gear will require a MUCH bigger starter motor. It can be done but the weight penalty might be too extreme. Now I see why you want to use NiCads for the power source. Basically you're asking an electric motor to a)power the bike and b)start the gas engine AT THE SAME TIME. That's gonna hurt.

I don't think the practice will help you any though. The start will take so long to build up engine revs that you'll lose any benefit almost immediately due to the bogged down engine trying to spin up to speed. One way it might work would be to hook the starter up to the chain, power up with the starter motor WITH THE CLUTCH DISCONNECTED and then pop the clutch when you get to around 5 mph. Of course if it fails to start you're in deep doo doo.

Still I think you're chasing decimals here. Best bet is to start the motor normally and then take off.